In the field of magnetic recording media, and particular in the field of magnetic disks, an MF-2HD floppy disk of 2 MB using Co-modified iron oxide has been standard-mounded on a personal computer. However, in the recent rapidly increasing the data capacity to be handled, the capacity of the floppy disk is not said to be sufficient and the increase of the capacity of a floppy disk has been desired.
Hitherto, as a magnetic recording medium, a magnetic recording medium formed by coating on a non-magnetic support a magnetic layer formed by dispersing an iron oxide, a Co-modified iron oxide, a ferromagnetic metal powder, or a hexagonal system ferrite fine powder in a binder has been widely used. In these magnetic powders, it is well-known that the ferromagnetic metal fine powder and the hexagonal system ferrite fine powder are excellent in the high-density recording characteristics.
As the large-capacity magnetic recording disk using the ferromagnetic metal fine powder excellent in the high-density recording characteristics, there are MF-2TD of 10 MB and MF-2SD of 21 MB and as the large-capacity magnetic recording disk using the hexagonal system ferrite fine powder excellent in the high-density recording characteristics, there are MF-2ED of 4 MB, 21 MB floptical, etc., but they are yet insufficient in the capacity and the performance.
Since hexagonal ferrite has a perpendicular anisotropy, it is said to be suitable for high-density recording. In JP-A-59-77628, JP-A-61-296525, JP-A-62-287420 and JP-A-62-109226 (the term "JP-A" as used therein means an "unexamined published Japanese patent application"), disk-shaped magnetic recording media each containing perpendicularly oriented hexagonal system ferrite are proposed.
The perpendicularly oriented hexagonal system ferrite are certainly excellent in the output and D50 (recording density) but there is a case that the error rate, which finally becomes important as the digital recording characteristics is rather greatly inferior. The reason is considered to be that when the disk-shaped magnetic recording medium is recorded and reproduced on the ring head in the case of having many perpendicular magnetization components, the wave form becomes a die pulse form, whereby an accurate peak cannot be detected. In the case of being randomly oriented, the hexagonal system ferrite has relatively many magnetization components in the perpendicular direction, whereby an under shoot occurs to form a wave form having an inferior symmetrical property and a similar problem to above occurs.
These problems described above become an obstacle to the practical use of hexagonal system ferrite having many perpendicular magnetization components. On the other hand, it has been investigated that perpendicular recording is performed using a single magnetic head and a wave form is made a single peak pulse but there are many problems for reaching a practically useful level.
As constitution of a disk-form magnetic recording medium having a non-magnetic undercoating layer or interlayer, there are proposed a constitution having an electrically conductive layer and a magnetic layer containing a metal fine powder as described in JP-A-3-120613, a constitution having a magnetic layer having a thickness of 1 .mu.m or less and a non-magnetic layer as described in JP-A-6-290446, a constitution having a carbon interlayer and a magnetic layer containing a lubricant as described in JP-A-62-159337, and a constitution having a non-magnetic layer wherein the carbon size is regulated as described in JP-A-5-290358.
On the other hand, recently, a disk-shaped magnetic recording medium comprising a thin magnetic layer and a functional non-magnetic layer has been developed and a floppy disk of a 100 MB class has appeared. As such the floppy disk showing the foregoing features there are proposed a constitution having a magnetic layer having Hc of 1400 Oe or more and a thickness of 0.5 .mu.m or less and a non-magnetic layer containing electrically conductive particles as described in JP-A-5-109061, a constitution containing abrasive having a larger size than the thickness of the magnetic layer thereof as described in JP-A-5-197946, a constitution having a magnetic layer having a thickness of 0.5 .mu.m or less, wherein the thickness deviation of the magnetic layer is restricted within .+-.15% and the surface electric resistance is regulated as described in JP-A-5-290354, and a constitution containing 2 kinds of abrasive each having different particle sizes and wherein the amounts of the abrasive on the surface are regulated as described in JP-A-6-68453.
However, with the recent rapid requirement of more increasing the recording density of a disk-shaped magnetic recording medium, even by using the techniques described above, it becomes difficult to obtain the disk-shaped magnetic recording medium having sufficient characteristics, that is, the characteristics of high-density recording and showing a low error rate. As one of the causes, there is a cause that the general relation paying attention to each element in the magnetic recording medium having the thin magnetic layer as described above relating the mode of a digital signal and the mode of the electromagnetic characteristics of the magnetic recording medium to said magnetic layer thickness has not yet been found.